The invention described here is a new variety of apple tree rootstock, Malus domestica×Malus robusta hybrid, hereinafter referred to as ‘G.41’. ‘G.41’ originated from a planned cross in 1975 in Geneva, N.Y. The new variety is a dwarfing rootstock that is resistant to fire blight and crown rot. It is precocious and highly productive, and can be used as a rootstock as well as for interstems of apple trees.
In the spring of 1975, pollen from a Malus robusta ‘Robusta 5’ apple tree was applied to emasculated flowers of a Malus domestica ‘Malling 27’ apple tree at the New York State Agricultural Experiment Station (“NYSAES”), Cornell University, Geneva, N.Y. In the fall of 1975, approximately 500 seeds resulting from this pollination were extracted from mature fruit derived from this cross. In the winter of 1975-76, the seeds were stratified and planted in large flats under conditions effective to germinate seeds and obtain seedlings. When germinated seedlings were about 2.5 cm tall they were inoculated with a mixture of isolates of the fungus Phytophthora cactorum (the causal agent of crown and root rots). The flats were flooded to mid-hypocotyl level and kept at 23° C. for one week. Surviving seedlings were transplanted into individual pots.
In the summer of 1976, each of the transplanted seedlings was inoculated with approximately 106 colony forming units of the Ea 273 strain of the fire blight bacterium Erwinia amylovora by inserting a 26-gauge hypodermic syringe needle into the shoot tip. The seedling designated at #041 was one of the survivors of this battery of inoculations from the same cross. All the surviving plants were transplanted to the Loomis field (NYSAES, Cornell University, Geneva, N.Y.) in the fall of 1976 and allowed to grow side shoots for propagation/evaluation. In 1978, ‘G.41’ was evaluated for rooting ability, lack of spine production, and low root brittleness in a layering bed (stool bed). In 1982, 4 finished trees with ‘G.041’ rootstock were planted in a first test orchard on the Loomis farm (NYSAES, Cornell University, Geneva, N.Y.) with Malus domestica cv. ‘Northern Spy’ grafted onto this rootstock as the scion cultivar. In 1983, two trees of the ‘G.41’ rootstock were also planted with Malus domestica cv. ‘Golden Delicious’ as the scion cultivar. This rootstock performed well (top 20% of many rootstocks tested) in these first test trials and more material was propagated by stool bed to be entered into new trials at the Research South Farm (NYSAES, Cornell University, Geneva, N.Y.). The ‘G.41’ rootstock performed well with all the scion cultivars that were tested. In summer 2002, 40 rootstock liners were inoculated with four different strains of fire blight (ten liners per strain) in the Plant Genetic Resources Unit greenhouse (NYSAES, Cornell University, Geneva, N.Y.) of the U.S. Department of Agriculture Agricultural Research Service. As a result, the apple rootstock ‘G.41’ was classified as resistant to the most virulent strains of fire blight.
Asexual reproduction of the ‘G.41’ apple rootstock has been achieved using the traditional method of clonally propagating apple rootstocks. In particular, the original seedling of the ‘G.41’ apple rootstock was planted in the Loomis field (NYSAES, Cornell University, Geneva, N.Y.) and allowed to develop into a “mother plant.” The ‘G.41’ mother plant was then used to obtain rooted liners using conventional layering procedures. The resulting liners were then planted in a row to generate a layering stool bed (also referred to as the “mother stool bed”). The living tissues (i.e. leaves, stems, roots, buds, and spines) of the mother stool bed were observed to be identical to secondary and tertiary stool bed plants. In addition to conventional layering, the ‘G.41’ apple rootstock variety has been asexually reproduced by root cuttings, by budding and grafting onto seedling and clonal rootstocks, and by tissue culture. Observations of trees from these propagations indicate that all trees have proven true to type and identical in all appearances to the original tree.